Logarithmic periodic antenna having gradient, relative to ground plane, varying along length of antenna



Nov. 22,1966 G. BRAUN 3,287,731

LOGARITHMIC PERIODIC ANTENNA HAVING GRADIENT, RELATIVE To GROUND PLANE, VARYING ALONG LENGTH OF ANTENNA Filed Aug. 4, 1964 2 Sheets-Sheet 1 E m9 Fi .1 ZII g 0 5 1'0 1'5 2'0 2's-f(MHz)3'o 60 30 20 12 7\(m)10 Fig.2 40- I 0 5 1b 1 5 2'0 f (MHz) Nov. 22, 1966 G. BRAUN 3 LOGARITHMIG PERIODIC ANTENNA HAVING GRADIENT, RELATIVE TO GROUND PLANE, VARYING ALONG LENGTH OF ANTENNA Filed Aug. 4, 1964 2 Sheets-Sheet 2 United States Patent C Claims. oi. 343 792.s

The invention relates to a logarithmic periodic antenna for long distance communication, especially involving horizontal polarization in the range of short and ultrashort waves.

In short wave transmissions, with the great distances generally involved between the transmitter and the receiving station (called counter-station), the main beam direction is elevated at a certain inclination or angle (gradient angle), so that the signals are reflected on the ionosphere and on this reflected path reach the receiving station. The gradient angle of the radiation emitted from the transmitting antenna must, accordingly, be so correlated to the distance between transmitter and receiver and to the height of the reflecting layer of the ionosphere that the distance between the stations can be bridged with a minimum of reflections on the ionosphere.

In known logarithmic periodic antennas the individual radiating elements are arranged in a straight, inclined plane, so that for the entire antenna installation only a single,'practically constant gradient angle results. Since in general, as the distance of the receiving stations increases, short wave transmissions require higher frequencies and flatter and flatter gradient angles, with a single logarithmic periodic antenna the necessary variation of the gradient angle is not provided over the entire transmitter frequency range. In order to provide an optimum gradient angle for the various frequency ranges, it was necessary to set up several logarithmically periodic antennas, each with a different angle of inclination, which were to be respectively 'operatively connected for the particular frequency ranges. In such installations, however, the inherent advantage of the wide band characteristics of the antenna is substantially lost.

The invention has, in particular, among its objects, the elimination of the difiiculties arising in long distance'transmissions employing logarithmically periodic antennas. According to the invention this is achieved by an arrangement wherein, as viewed in the direction of the center line of the antenna, the inclination angle of the antenna system with respect to the surface of the earth is made greater for the radiating elements with greater transverse dimensions, and thereby larger operating wave lengths than for radiating elements with smaller transverse dimensions and thereby shorter operating wave lengths. The ratio of the height of the active radiating groups of the antenna to the wave lengths concerned is then no longer constant but is adapted to the necessary gradient angle.

Since within a single antenna, through the resulting curvature of the center line of the antenna installation, the optimum angle is achieved for each of the individual ranges, whereby the antenna installation becomes just as wide banded with respect to the inclination angle of the main beam as with respect to its frequency characteristics. Thereby a complete utilization is achieved of the possibilities available from the wide band properties of the logarithmically periodic antennas in conjunction with long distance transmission.

The center line of the antenna installation extending, in the case of horizontal polarization, in a vertical plane can be selected as a polygonal development which has in 'ice the individual partial ranges, for example in the lower, middle and upper operating frequency ranges, the desired gradient angle. Such an arrangement .is especially expedient in spatially extended logarithmically periodic antennas, in which the individual partial sections of the antennas are fixed in their position in a tensioned system by means of guy lines or the like. The invention also is applicable to antenna installations, which in themselves form rigid structures, as for example, in the case of antenna elements supported on a continuous longitudinal carrier, when in consequence of the dimensions or other design or construction requirements preference should be given to an antenna composed of several individual components. In all other cases there can be used instead of a center line representing a polygonal development, a continuously curved development, or one approximating the same.

In the drawings:

FIG. 1 is a chart illustrating the dependency of the antenna height on frequency; v

FIG. 2 is a similar chart illustrating the center line characteristics for an antenna with broad band characteristics;

FIG. 3 illustrates the gradient angle and corresponding half power width; and

FIG. 4 is an oblique view of an antenna installation embodying the invention.

In FIG. 1 the antenna height it (above the surface of the earth) is represented in meters in dependence on the frequency f in mc./s., or of wave length A. The most favorable gradient angle for the uppermost frequency range (about 14 and 30 mc./s.) is entered as a solid curve 1 and for the lower frequency range (about 4 and mc./s. as curve 2. It illustrates that for the longer wave lengths a greater gradient angle exists and for the shorter wave lengths a smaller gradient angle exists. The relation between the frequency ranges, the distance, the gradient angle and the half-power width, as well as of the height 11 (above the surface of the earth) in dependence on the wave length, is shown in the following table:

Gradient angle Distance, km. and half-power width On the assumption that the band width of a logarithmically periodic antenna extends from 5 to 30 mc./s., it follows from this representation that with a logarithmically periodic antenna arranged in one plane the requirements mentioned with respect to the beam angle can be fulfilled only for a certain frequency range. For all other values, however, there result deviations from the optimum gradient angle.

The desired radiation characteristic can, however, be achieved if the antenna is constructed according to a curve which is composed of the individual curves represented in the manner of a polygonal development. A course of the center line of the antenna installation is thereby attained such as is represented, for example, in FIG. 2. The individual radiating elements of the logarithmically periodic antenna now no longer lie in one plane, but in a curved surface the upper face of which is concave. The gradient angle over the frequency range of the antenna is then no longer constant, but has a course as designated in FIG. 3 by the numeral 3. The curves 3a and 3b give the corresponding half-power widths.

The construction of a logarithmically periodic antenna in which the principles described are applied is illustrated in FIG. 4. On the supporting masts 4 and 5 there is suspended from ropes or lines 6 and 7 the logarithmically periodic antenna installation 8, represented in heavy lines, whose apex end, active in the range of the short waves, is secured near the ground by a short mast piece 9. The thin lines 10 and 11 indicate the course of an antenna installation when, as in known systems, all the radiating elements lie in a single plane. In contrast thereto, in the antenna embodying the invention, the mid-line of the antenna installation is formed as a curve -or a polygonal development and the antenna lies in a convex curve, as seen from the ground. schematically illustrated guy ropes or lines 12 to 15 which are connected, for example over insulators, with the supporting ropes or lines 6 and 7, maintain the antenna installation in operative position.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

I claim:

1. A logarithmically periodic antenna for telecommunication, especially for horizontal polarization in the range of short and ultra short waves, comprising an arrangement of transmitter elements which are excited with respect to earth and constructed according to the log periodic law, the center line of the antenna being curved toward the surface of the earth, whereby the gradient angle of the antenna system with respect to the surface of the earth is greater for radiating elements with greater transverse dimensions, and thereby longer operating wave length, than ,for radiating elements with smaller transverse dimensions,

and thereby shorter operating wave length, said center line being formed with a curve that will provide at least approximately the desired gradient angle of the principal transmission lobe for each operating frequency.

2. An antenna according to claim 1, wherein the said center line extending in a vertical plane forms a polygonal development, which has the desired gradient angles in individual partial ranges, for example the lower, middle and upper operating frequency range of the antenna.

3. An antenna according to claim 2, wherein the center line development is formed as a continuous curve approximating the development determined from the individual ranges.

4. An antenna according to claim 3, wherein the antenna installation is concave in the direction of the surface of the earth.

5. An antenna according to claim 3, wherein the antenna is suspended from supporting carrying masts, and tensioned by insulated guy ropes.

References Cited by the Examiner UNITED STATES PATENTS 2,977,597 3/1961 Du Hamel et al. 343--792.5

HERMAN KARL SAALBACH, Primary Examiner. R. F. HUNT, JR., Assistant Examiner. 

1. A LOGARITHMICALLY PERIODIC ANTENNA FOR TELECOMMUNICATION, ESPECIALLY FOR HORIZONTAL POLARIZATION IN THE RANGE OF SHORT AND ULTRA SHORT WAVES, COMPRISING AN ARRANGEMENT OF TRANSMITTER ELEMENTS WITH ARE EXCITED WITH RESPECT TO EARTH AND CONSTRUCTED ACCORDING TO THE LOG PERIODIC LAW, THE CENTER LINE OF THE ANTENNA BEING CURVED TOWARD THE SURFACE OF THE EARTH, WHEREBY THE GRADIENT ANGLE OF THE ANTENNA SYSTEM WITH RESPECT TO THE SURFACE OF THE EARTH IS GREATER FOR RADIATING ELEMENTS WITH GREATER TRANSVERSE DIMENSIONS, AND THEREBY LONGER OPERATING WAVE LENGTH,THAN FOR RADIATING ELEMENTS WITH SMALLER TRANSVERSE DIMENSIONS, AND THEREBY SHORTER OPERATING WAVE LENGTH, SAID CENTER LINE BEING FORMED WITH A CURVED THAT WILL PROVIDE AT LEAST APPROXIMATELY THE DESIRED GRADIENT ANGLE OF THE PRINCIPAL TRANSMISSION LOBE FOR EACH OPERATING FREQUENCY. 